1. Field of the Invention
The present invention relates to an integrated circuit and a resonance circuit.
2. Description of the Related Art
Following rapid development of mobile communication, radio waves of an extremely wide range of frequencies are required in recent years, and the frequencies of the radio waves employed for mobile communication are now shifting to the microwave band. Therefore, an amplifier employed for a portable terminal is formed by a monolithic microwave integrated circuit (MMIC) or a modularized microwave integrated circuit (MIC).
An amplifier for amplifying a signal of a desired frequency employs a bias circuit for applying a prescribed dc bias to the gate or the drain of a field-effect transistor (FET). The amplifier is further provided with a feedback circuit for preventing the FET from oscillating in a low-frequency domain and improving the stability of the amplifier.
FIG. 23 is a circuit diagram showing an exemplary conventional bias circuit which is provided on an amplifier formed by an FET 200.
The bias circuit shown in FIG. 23 comprises a parallel resonance circuit 300 formed by an inductor L1 and a capacitor C1, which are connected in parallel with each other. This parallel resonance circuit 300 can apply a dc drain bias Vd to the drain of the FET 200 from a bias supply by adjusting the inductance value of the inductor L1 and the capacitance value of the capacitor C1, without passing a signal of a desired frequency.
When the amplifier is employed in the 1.5 GHz band, for example, the parallel resonance circuit 300 can apply the drain bias Vd to the drain of the FET 200 with no signal loss at the frequency of 1.5 GHz by setting the inductance value of the inductor L1 and the capacitance value of the capacitor C1 at 0.4 nH and 28 pF, respectively.
FIG. 24 is a circuit diagram showing another exemplary bias circuit provided on an amplifier which is formed by an FET 200.
The bias circuit shown in FIG. 24 is formed by a microstrip line MSL. This microstrip line MSL can apply a dc drain bias Vd to the drain of the FET 200 by setting its length at xc2xc the wavelength corresponding to a desired frequency, without passing a signal of the frequency.
FIG. 25 is a circuit diagram showing an exemplary conventional feedback circuit provided on an amplifier which is formed by an FET 200.
The feedback circuit shown in FIG. 25 is formed by a capacitor C2 and a resistor R1, which are serially connected between the drain and the gate of the FET 200. This feedback circuit feeds back a part of a high-frequency signal appearing on the drain of the FET 200 to the gate in a negative phase. Thus, the feedback circuit suppresses the gain mainly at a low frequency and prevents the FET 200 from oscillation. The capacitor C2 is so provided as to feed back no dc component to the gate of the FET 200.
The bias circuit shown in FIG. 23 formed by the parallel resonance circuit 300 requires at least two types of elements, i.e., the inductor L1 and the capacitor C1. When the amplifier is designed, therefore, a space for mounting the inductor L1 and the capacitor C1 must be provided on a substrate.
Particularly in case of an MMIC operating in a high-frequency region, a spiral inductor having a large occupied area is employed as the inductor L1. Therefore, the area of the parallel resonance circuit formed on a dielectric substrate is extremely increased.
On the other hand, a modularized MIC requires external parts called a chip capacitor and a chip inductor as the capacitor C1 and the inductor L1 respectively. In this case, it is necessary to consider a method of adjacently mounting the chip capacitor and the chip inductor in the vicinity of each other. Thus, the bias circuit occupies an extremely large area on a substrate, and exerts bad influence on the characteristics of the modularized MIC. Further, the chip inductor is considerably high-priced as compared with the chip capacitor.
In addition, a wire having a finite length is present for connecting the drain of the FET 200 with the bias supply. This wire is formed by a microstrip line on a dielectric substrate. Thus, the calculative resonance frequency of the parallel resonance circuit 300 deviates from the actual one due to the presence of the microstrip line. Therefore, the parallel resonance circuit 300 must be designed in consideration of the microstrip line.
In the bias circuit formed by the microstrip line MSL shown in FIG. 24, the length of the microstrip line MSL is disadvantageously increased. Assuming that a dielectric substrate has a thickness of 0.8 mm and a dielectric constant of 9 in case of employing the bias circuit at a frequency of 1.5 GHz, for example, the length equal to xc2xc the wavelength is about 20 mm.
The feedback circuit shown in FIG. 25 formed by the resistor R1 and the capacitor C2 requires at least two types of elements. If the resistance value of the resistor R1 is reduced in order to improve stability in this feedback circuit, the feedback amount is increased to disadvantageously reduce the gain. If the resistance value of the resistor R1 is increased, on the other hand, the feedback effect is reduced and the stability cannot be improved.
To this end, the feedback circuit may be provided with a parallel resonance circuit formed by an inductor and a capacitor, to be capable of feeding back only a signal of a frequency other than the desired frequency. Thus, reduction of the gain can be suppressed with respect to the signal of the desired frequency while reducing the resistance value of the resistor R1.
However, such provision of the parallel resonance circuit formed by the inductor and the capacitor results in a problem absolutely similar to that in the bias circuit shown in FIG. 23, and allows no miniaturization. Further, a wire having a finite length is necessarily present, in order to connect the drain and the gate of the FET 200. This wire is formed by a microstrip line on a dielectric substrate as hereinabove described, and hence the calculative resonance frequency of the parallel resonance circuit disadvantageously deviates from the actual one.
An object of the present invention is to provide an integrated circuit allowing miniaturization and having excellent characteristics, which can be fabricated with a small number of elements through simple steps.
Another object of the present invention is to provide a resonance circuit allowing miniaturization and having excellent characteristics, which can be fabricated with a small number of elements through simple steps, and a bias circuit, a feedback circuit, a high-frequency signal processing circuit, a matching circuit and a stub comprising the same.
An integrated circuit according to an aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate, and a capacitor which is arranged on the microstrip line and connected to this microstrip line.
The microstrip line is inductive or capacitive, depending on the relation between its length and a frequency. In the integrated circuit according to the present invention, therefore, the length of the microstrip line is set so that the microstrip line is inductive at a specific frequency, thereby forming a parallel circuit of an inductance and a capacitance.
In this case, the parallel circuit of the inductance and the capacitance can be formed in a small occupied area with a small number of elements through simple steps, since the capacitor is arranged on the microstrip line.
The microstrip line may include a microstrip conductor and a grounding conductor which are formed on the front and back surfaces of the dielectric substrate respectively, and the capacitor may include a dielectric material which is arranged on the microstrip conductor and a pair of electrodes which are provided on both ends of the dielectric material along the longitudinal direction of the microstrip conductor, so that the pair of electrodes are connected to the microstrip conductor respectively.
In this case, the resonance frequency of the parallel circuit is univocally set by the length of the microstrip conductor between the pair of electrodes of the capacitor, the dielectric constant and the thickness of the dielectric substrate and the capacitance value of the capacitor. Therefore, the resonance frequency can be readily matched with a desired frequency.
Alternatively, the microstrip line may include a microstrip conductor and a grounding conductor which are formed on the front and back surfaces of the dielectric substrate respectively, and the capacitor may include an insulator layer which is formed on the microstrip conductor and a metal layer which is formed on the insulator layer, so that an end of the metal layer along the longitudinal direction of the microstrip conductor is connected to the microstrip conductor.
In this case, the resonance frequency of the parallel circuit is univocally decided by the length of the microstrip conductor located under the metal layer, the dielectric constant and the thickness of the dielectric substrate and the capacitance value of the capacitor. Therefore, the resonance frequency can be readily matched with a desired frequency.
In particular, the capacitance value of the capacitor, which can be set by adjusting the thickness of the insulator layer, is hardly limited by any dimension.
A resonance circuit according to another aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate, and a capacitor which is arranged on the microstrip line and connected with this microstrip line.
The resonance circuit can resonate at a specific frequency by setting the length of the microstrip line so that the microstrip line is inductive at the specific frequency.
In this case, the resonance frequency, which is univocally decided by the capacitance value of the capacitor and the characteristics of the microstrip line, can be readily matched with a desired frequency. Thus, excellent characteristics can be readily implemented.
Further, the capacitor is arranged on the microstrip line, whereby the resonance circuit can be fabricated in a small occupied area with a small number of elements through simple steps.
The microstrip line may include a microstrip conductor and a grounding conductor which are formed on the front and back surfaces of the dielectric substrate respectively, and the capacitor may include a dielectric material which is arranged on the microstrip conductor and a pair of electrodes which are provided on both ends of the dielectric material along the longitudinal direction of the microstrip conductor, so that the pair of electrodes are connected to the microstrip conductor respectively.
In this case, the resonance frequency is univocally decided by the length of the microstrip conductor between the pair of electrodes of the capacitor, the dielectric constant and the thickness of the dielectric substrate and the capacitance value of the capacitor. Therefore, the resonance frequency can be readily matched with the desired frequency.
The length between the pair of electrodes of the capacitor which are connected to the microstrip conductor may be set so that the microstrip line is inductive with respect to the specific frequency.
In this case, the microstrip line is inductive with respect to the specific frequency, whereby the resonance circuit can resonate at the desired frequency by adjusting the capacitance value of the capacitor.
The capacitance value of the capacitor may be so set as to cause resonance at the aforementioned specific frequency. Thus, the resonance circuit can resonate at the desired frequency.
Alternatively, the microstrip line may include a microstrip conductor and a grounding conductor which are formed on the front and back surfaces of the dielectric substrate respectively, and the capacitor may include an insulator layer which is formed on the microstrip conductor and a metal layer which is formed on the insulator layer so that an end of the metal layer along the longitudinal direction of the microstrip conductor is connected to the microstrip conductor.
In this case, the resonance frequency is univocally decided by the length of the microstrip conductor located under the metal layer, the dielectric constant and the thickness of the dielectric substrate and the capacitance value of the capacitor. Therefore, the resonance frequency can be readily matched with the desired frequency.
In particular, the capacitance value of the capacitor, which can be set by adjusting the thickness of the insulator layer, is hardly limited by any dimension.
The length of the metal layer along the longitudinal direction of the microstrip conductor may be set so that the microstrip line is inductive with respect to the specific frequency.
In this case, the microstrip line is inductive with respect to the specific frequency, whereby the resonance circuit can resonate at the desired frequency by setting the capacitance value of the capacitor.
The capacitance value of the capacitor may be so set as to cause resonance at the aforementioned specific frequency. Thus, the resonance circuit can resonate at the desired frequency.
A bias circuit for applying a bias to an electrode of a transistor according to still another aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and connected to the electrode of the transistor, and a capacitor which is arranged on the microstrip line and connected to the microstrip line, to apply the bias to a part of the microstrip line which is opposite to the transistor in relation to the capacitor.
In this case, a resonance circuit formed by the microstrip line and the capacitor can open at a prescribed frequency by setting the capacitance value of the capacitor to cause resonance at the prescribed frequency. Thus, the bias circuit can apply the bias to the electrode of the transistor through the microstrip line without influencing a signal of the prescribed frequency on the electrode of the transistor.
An electrode of the capacitor closer to the transistor is connected to a position excluding that separating from the electrode of the transistor by a distance equal to xc2xc the wavelength corresponding to the prescribed frequency on the microstrip line. Thus, the electrode of the transistor is not shorted with respect to the prescribed frequency.
A bias circuit for applying a bias to an electrode of a transistor according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and connected to the electrode of the transistor, and a capacitor which is arranged on the microstrip line and connected to this microstrip line. An electrode of the capacitor which is opposite to the transistor is grounded in a high-frequency manner, so that the bias is applied to a part of the microstrip line which is opposite to the transistor in relation to the capacitor.
In this case, a resonance circuit formed by the microstrip line and the capacitor can be set at a prescribed impedance by setting the capacitance value of the capacitor to cause resonance at a prescribed frequency. Thus, the bias circuit can apply the bias to the electrode of the transistor through the microstrip line without influencing a signal of the prescribed frequency on the electrode of the transistor.
The electrode of the capacitor which is opposite to the transistor may be grounded through a bypass capacitor. Thus, the electrode of the capacitor which is opposite to the transistor is grounded in an ac manner.
A feedback circuit, which is provided between output- and input-side electrodes of a transistor, according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate for feeding back a signal on the output-side electrode of the transistor to the input-side electrode, and a capacitor which is arranged on the microstrip line and connected to this microstrip line.
In this feedback circuit, a signal of a specific frequency among those outputted from the output-side electrode of the transistor is blocked by a resonance circuit which is formed by the microstrip line and the capacitor not to be fed back to the input-side electrode, while the remaining signal of another frequency is fed back to the input-side electrode. Thus, the stability of the transistor is improved.
A high-frequency signal processing circuit, which is connected to a prescribed node for suppressing a specific frequency signal, according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and connected to the prescribed node, and a capacitor which is arranged on the microstrip line and connected to this microstrip line, and an electrode of the capacitor which is opposite to the prescribed node is grounded in a high-frequency manner. The capacitance value of the capacitor is so set as to cause resonance at the specific frequency. Thus, the high-frequency signal processing circuit suppresses the specific frequency signal.
A matching circuit, which is connected to a prescribed circuit, according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and connected to the prescribed circuit, and a capacitor which is arranged on the microstrip line and connected to this microstrip line.
This matching circuit can attain impedance matching with the prescribed circuit by adjusting the position of the capacitor which is arranged on the microstrip line.
A stub, which extends from a prescribed line to open with respect to a specific frequency, according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and extends from the prescribed line, and a capacitor which is arranged on the microstrip line and connected to this microstrip line. The capacitance value of the capacitor is set to cause resonance at the specific frequency. Thus, a resonance circuit which is formed by the microstrip line and the capacitor opens at the specific frequency.
A stub, which extends from a prescribed line and terminates the prescribed line at a prescribed impedance with respect to a specific frequency, according to a further aspect of the present invention comprises a dielectric substrate, a microstrip line which is provided on the dielectric substrate and extends from the prescribed line, and a capacitor which is arranged on the microstrip line and connected to this microstrip line, and an electrode of the capacitor which is opposite to the prescribed line is grounded in a high-frequency manner. The capacitance value of the capacitor is set to cause resonance at the specific frequency. Thus, a resonance circuit which is formed by the microstrip line and the capacitor is at a prescribed impedance with respect to the specific frequency.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.